Sheet feeder, image reading apparatus and image forming apparatus

ABSTRACT

A paper press member  240  configured to be capable of advancing and retracting with respect to a paper guide  220  is provided between a paper feed roller  234  and the front end in the paper feed direction of paper loaded in a manual feed tray  230 . When a plurality of sheets of paper enter into the press-contact section between the paper feed roller  234  and a reverse roller  235 , the reverse roller  235  is rotated in the reverse direction to retract the sheet on the reverse roller side to the manual feed tray  230 . At this time, by causing the paper press member  240  to project from the upper surface of the paper guide  220 , the sheet to be retracted and the paper press member  240  come into contact with each other, so that the travel amount of the sheet when retracting the sheet is reduced.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a)on Patent Application No. 2007-124930 filed in Japan on May 9, 2007, theentire contents of which are hereby incorporated by reference.

BACKGROUND

1. Technical Field

The present application relates to a sheet feeder capable of certainlypreventing multi-feeds (feeding two or more sheets at a time), and animage reading apparatus and an image forming apparatus comprising thesheet feeder.

2. Description of Related Art

As the paper feeding system in an image forming apparatus, two types offeeding systems are used. One is a paper feeding cassette system inwhich one sheet of paper is taken out of the paper feeding cassette atone time and fed to a printing section, and the other is a manualfeedtray system in which paper of irregular size, or only a small amountof paper to be used, is loaded in the manual feed tray, and the paper istaken out of the manual feed tray and supplied to the printing section.

Since a number of sheets of paper corresponding to a print request areoften loaded in the manual feed tray, the load of paper in the manualfeed tray is small. However, with high-speed processing (high-speedimage processing, high-speed print processing etc.) in recent years,there is a tendency toward an increase in the load of paper in themanual feed tray. FIG. 1 is a schematic view showing a schematicstructure of a conventional manual paper feed unit, and FIGS. 2A to 2Care explanatory views for explaining the operation of the manual paperfeed unit. A manual paper feed unit 53 shown in FIG. 1 comprises amanual feed tray 530 for loading paper, and a paper regulating plate 531for preventing skew of the transported paper by being adjusted suitablyaccording to the paper size. In order to regulate the paper loadposition in the direction orthogonal to the paper feed direction, thepaper regulating plate 531 is configured to be able to slide in theabove-mentioned direction with a mechanism such as, for example, lackand pinion gears.

Thus, in the direction orthogonal to the paper feed direction, the paperposition is regulated by the paper regulating plate 531. However, amember for regulating the paper position is not generally provided forthe paper feed direction (particularly for the rear end of the paperloaded in the manual feed tray 530). In other words, in order to avoidpaper feeding errors, the manual feed tray 530 is arranged on a sideface of an apparatus in an inclined manner so that the paper loadingsurface is lower on the apparatus side and higher on the rear end sideof the loaded paper. Since the paper feed performance is improved, it isnot necessarily to regulate the position of the rear end of the paper.

In such a manual feed tray 530, when a large amount of paper is loadedand a large amount of paper is used for one printing as in recent days,like the above-mentioned paper feeding cassette system, frictionalelectrification occurs between a sheet P1 to be taken out by a pickuproller 532 and a sheet P2 to be fed next, and the frictionallyelectrified charge accumulates in the paper loading section, and thusthere is a possibility that a multi-feed in which a plurality of sheetsof paper are simultaneously fed may occur in feeding the paper (see FIG.2A). If the paper is transported to the printing section in themulti-feed condition, not only the print quality is degraded, but alsofriction with peripheral members may cause a paper jam and damage to theperipheral members.

Therefore, in the manual paper feed unit 53, the sheet P1 taken out ofthe manual feed tray 530 and the sheet P2 to be fed next are separatedusing a paper feed roller 534 and an opposing reverse roller 535 pressedagainst the paper feed roller 534, so that one sheet of paper istransported to the printing section. The reverse roller 535 is notalways rotated in the reverse direction during the paper feedingprocess, but is rotated in the reverse direction when a predeterminedload is applied to a torque limiter placed on the rotation shaft of thereverse roller 535 and the shaft axis is coupled to the driving shaft.Hence, during normal feed in which one sheet is transported, since thedriving load is small, the driving shaft is not coupled to and thereverse roller 535 is rotated according to the paper feed roller 534. Onthe other hand, during multi-feed in which a plurality of sheets ofpaper are fed at a time, since the driving load is large, the drivingshaft is coupled to and the reverse roller 535 is rotated in thedirection opposite to the rotation direction of the paper feed roller534 (see FIG. 2B).

Since the paper feed roller 534 and the reverse roller 535 are rotatedin mutually opposite directions, the fed sheet on the paper feed roller534 side is transported to the downstream side in the paper feeddirection and transported to the printing section as a predeterminedsupply destination, while the fed sheet on the reverse roller 535 sideis transported to the upstream side in the paper feed direction andreturned to the manual feed tray 530.

When retracting the extra sheet fed by the multi-feed to the manual feedtray 530 by the function of the reverse roller 535, the travel amount(return amount) varies depending on the type of paper. In other words,when the rotation speed of the reverse roller 535 is fixed, the function(returning force) acting on the paper is fixed. Therefore, if the typeof paper is thin paper, since the paper has small flexibility, thereturning force is not sufficiently transmitted, the paper is bucked,and the return amount is relatively small. In this case, since themulti-feed problem is solved by slightly retracting the sheet from thepaper feed roller 534 to the upstream side, a multi-feed does not occurwhen feeding the next sheet.

However, when the paper type is thick paper, the paper has strongflexibility, and therefore the returning force of the reverse roller isdirectly transmitted to the paper and the return amount is large. Inparticular, when the paper is small-sized thick paper such as a postcard, since the weight of the paper is light with respect to thereturning force, the return amount is large and the following problemoccurs.

Specifically, as shown in FIG. 2C, if the front end in the sheet feeddirection of the sheet P2 to be moved back to the manual feed tray 530returns upstream of the point where the pickup roller 532 is loweredwhen feeding paper, a sheet P3 placed under the returned sheet P2 ispicked up by the pickup roller 532 in the next paper feeding process andtwo sheets P2 and P3 are fed at one time, and thus a multi-feed occursdefinitely.

SUMMARY

The present application has been made with the aim of solving the aboveproblems, and it is an object of the present application to provide asheet feeder comprising, between a paper feed roller and the front endof a stored sheet in a sheet feed direction, a contact member configuredto be capable of advancing and retracting and capable of coming intocontact with an extra sheet fed by a multi-feed, and thereby capable ofreducing the travel amount of sheet when retracting the extra sheet fedby the multi-feed and capable of certainly preventing multi-feeds, andto provide an image reading apparatus and an image forming apparatuscomprising the sheet feeder.

A sheet feeder according to the present application is a sheet feedercomprising: a sheet storing section for storing sheets; a paper feedroller for feeding a sheet taken out of the sheet storing section to apredetermined supply destination; detecting section for detecting amulti-feed of sheets in the paper feed roller; and a sheet retractingunit for retracting, when the detecting means detects a multi-feed ofsheets, an extra sheet fed by the multi-feed to an upstream side in asheet feed direction, and characterized by comprising, between the paperfeed roller and the front end in the sheet feed direction of the sheetstored in the sheet storing section, a contact member configured to becapable of advancing and retracting and capable of coming into contactwith an extra sheet fed by a multi-feed.

In this application, since the contact member capable of advancing andretracting and capable of coming into contact with the sheet fed by amulti-feed is provided between the paper feed roller and the front endof the stored sheet in the sheet feed direction, it is possible toreduce the travel amount of sheet when retracting the sheet fed by themulti-feed to the sheet storing section, and it is possible to prevent amulti-feed in the next paper feeding process.

The sheet feeder according to the present application is characterizedin that the contact member comes into contact with the front surface orthe back surface of the extra sheet when retracting the sheet.

In this application, since the contact member is configured to come intocontact with the front surface or the back surface of the sheet whenretracting the sheet, friction is caused between the contact member andthe sheet to be retracted when a multi-feed of sheets occurs.

The sheet feeder according to the present application is characterizedby further comprising a driving section for moving, when feeding a sheetto the supply destination, said contact member not to come into contactwith the sheet, and for moving, when said detecting means detects amulti-feed of sheets, said contact member to come into contact with theextra sheet fed by the multi-feed.

In this application, since the contact member is configured to beseparated from a sheet during normal feeding and come into contact witha sheet when a multi-feed is detected, the transport operation in thenormal paper feeding process is not interfered, and the travel amount ofsheet when retracting the sheet is reduced by bringing the contactmember into contact with the sheet only when a multi-feed occurs.

The sheet feeder according to the present application is characterizedin that the sheet retracting unit includes a reverse roller placedopposite to the paper feed roller, and a torque limiter supported on adriving shaft of the reverse roller, wherein when the torque limiterdetects an increase in load and the reverse roller is coupled to a drivesource and starts to be driven, the detecting means determines that amulti-feed was detected.

In this application, a multi-feed is detected by detecting a rotation ofthe reverse roller which is conventionally provided to separate sheetsfed by a multi-feed.

The sheet feeder according to the present application is characterizedin that the travel amount of sheet when the sheet retracting unitretracts the sheet is restrained by the contact between the sheet andthe contact member.

In this application, since the travel amount of sheet when retractingthe sheet is restrained by the contact between the sheet and the contactmember, the possibility of reoccurrence of multi-feed in the next paperfeeding process is decreased.

The sheet feeder according to the present application is characterizedby comprising a pickup roller arranged to be able to come into contactwith the sheet stored in the sheet storing section, wherein the sheetfeeder restrains the front end in the feed direction of a sheet to beretracted from returning upstream of a contact section between thepickup roller and the sheet stored in the sheet storing section.

In this application, since returning of the sheet to the upstream of thecontact section between the pickup roller and the stored sheet isrestrained, a sheet to be fed in the next paper feeding process is thesheet retracted by the retracting means.

The sheet feeder according to the present application is characterizedin that the contact member has elasticity.

In this application, by using an elastic member, such as rubber, foamsponge, and cork, as the contact member, even if the contact member isbrought into contact with a sheet to be retracted, there is nopossibility that the sheet is damaged or torn, and it is possible toprevent wasteful disposal of sheets and degradation of the printquality.

The sheet feeder according to the present application is characterizedin that the sheet storing section is a manual feed tray.

In this application, by applying the sheet feeder to a manual feed trayhaving no regulating member for regulating the position of the rear endof a sheet in the sheet feeding direction, it is possible to reduce theoccurrence of multi-feeds in the paper feed unit of the manual feedtray.

An image reading apparatus according to the present application ischaracterized by comprising: a sheet feeder of the above-mentionedapplication; and image reading means for reading an image recorded on asheet fed by the sheet feeder.

In this application, since multi-feeds are prevented, the processingefficiency is not decreased even when reading a large amount of images.

An image forming apparatus according to the present application ischaracterized by comprising: a sheet feeder of the above-describedapplication; and image forming means for forming an image on a sheet fedby the sheet feeder.

In this application, since multi-feeds are prevented, the processingefficiency is not decreased even when printing a large amount of images.

According to the present application, since the contact member capableof advancing and retracting and capable of coming into contact with anextra sheet fed by a multi-feed is provided between the paper feedroller and the front end of the stored sheet in the sheet feeddirection, it is possible to reduce the travel amount of sheet whenretracting the sheet fed by the multi-feed to the sheet storing section,and it is possible to prevent a multi-feed in the next paper feedingprocess.

According to the present application, since the contact member isconfigured to come into contact with the front surface or back surfaceof a sheet when retracting the sheet, it is possible to reduce thetravel amount of sheet when retracting the sheet by the friction betweenthe contact member and the front surface or back surface of the sheet.

According to the present application, since the contact member isconfigured to be separated from a sheet during normal feeding and comeinto contact with a sheet when a multi-feed is detected, the transportoperation in the normal paper feeding process is not interfered, and itis possible to reduce the travel amount of sheet when retracting thesheet by bringing the contact member into contact with the sheet onlywhen a multi-feed occurs.

According to the present application, it is possible to detect amulti-feed by detecting a rotation of the reverse roller which isconventionally provided to separate sheets fed by the multi-feed.

According to the present application, since the travel amount of sheetwhen retracting the sheet is restrained by the contact between the sheetand the contact member, it is possible to decrease the possibility ofreoccurrence of multi-feed in the next paper feeding process.

According to the present application, since returning of the sheet tothe upstream of the contact section between the pickup roller and thestored sheet is restrained, the sheet retracted by the retracting meansis certainly transported in the next paper feeding process, and thus itis possible to prevent reoccurrence of multi-feed.

According to the present application, by using an elastic member such asrubber, foam sponge, and cork as the contact member, even if the contactmember is brought into contact with a sheet to be retracted, there is nopossibility that the sheet is damaged or torn, and thus it is possibleto prevent wasteful disposal of sheets and degradation of the printquality.

According to the present application, by applying the sheet feeder to amanual feed tray having no regulating member for regulating the positionof the rear end of a sheet in the sheet feeding direction, it ispossible to reduce the occurrence of multi-feeds in the paper feed unitof the manual feed tray.

According to the present application, since it is possible to preventmulti-feeds, it is possible to automatically read a large amount ofimages without decreasing the processing efficiency.

According to the present application, since it is possible to preventmulti-feeds, it is possible to print a large amount of images at a timewithout decreasing the processing efficiency.

The above and further objects and features of the application will morefully be apparent from the following detailed description withaccompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic view showing a schematic structure of aconventional manual paper feed unit;

FIGS. 2A to 2C are explanatory views for explaining the operation of themanual paper feed unit;

FIG. 3 is a cross sectional view showing the entire structure of adigital all-in-one apparatus comprising a sheet feeder according to thepresent application;

FIG. 4 is a schematic view for explaining the structure of a manualpaper feed unit according to an embodiment;

FIGS. 5A and 5B are schematic views showing the structure of a paperpress member;

FIGS. 6A to 6C are explanatory views for explaining an operationperformed by the manual paper feed unit when a multi-feed occurs;

FIGS. 7A to 7C are explanatory views for explaining an operationperformed by the manual paper feed unit when a multi-feed occurs;

FIG. 8 is a block diagram showing the structure of a control system ofthe manual paper feed unit; and

FIG. 9 is a flowchart showing the steps of a paper feeding processperformed by the manual paper feed unit.

DETAILED DESCRIPTION

The following description will explain in detail the presentapplication, based on the drawings illustrating an embodiment thereof.

FIG. 3 is a cross sectional view showing the entire structure of adigital all-in-one apparatus comprising a sheet feeder according to thepresent application. The digital all-in-one apparatus shown in FIG. 3comprises a printer unit 1 for forming an image on a sheet of paper, OHPfilm etc. (hereinafter just referred to as the paper); a paper feed unit2 for supplying the paper to the printer unit 1; and a scanner unit 3for generating image data by optically reading a document image.

The scanner unit 3 comprises a light source unit 32, a mirror unit 33and a reading unit 34 as optical image reading means. The light sourceunit 32 applies reading light to a document placed on a document platen31, or a document sent from an automatic document feeder 35. The mirrorunit 33 comprises a pair of mirrors whose reflection surfaces placed ata right angle to each other to guide reflected light from the documentto the reading unit 34. The reading unit 34 comprises a reading element,such as a CCD, for converting the light guided by the mirror unit 33into an analog signal; an AD converter for converting the analog signalobtained by the reading element into a digital signal; and a DSP forcorrecting the converted digital signal, based on the variation in thesensitivity of the CCD etc., and outputting the resulting signal asimage data.

The printer unit 1 comprises an exposure unit 10, a developing device11, a photosensitive drum 12, an electrifier 13, a cleaner unit 14, atransfer unit 15, and a fixing unit 16, and forms an image on paper fedfrom the paper feed unit 2, based on image data generated in the scannerunit 3, or print data obtained by communication means, not shown.

The exposure unit 10 comprises a laser scanning unit (LSU) including alaser irradiating section and a reflection mirror, and exposes thephotosensitive drum 12 charged evenly by the electrifier 13 to light,according to the inputted image data, thereby forming an electrostaticlatent image on the surface of the photosensitive drum 12 according tothe image data. The electrifier 13 is electrifying means for evenlycharging the surface of the photosensitive drum 12 to a predeterminedelectric potential, and, for example, a charger type electrifier isused.

The developing device 11 visualizes the electrostatic latent imageformed on the photosensitive drum 12 with toner as developer. Thecleaner unit 14 removes and collects the toner remaining on the surfaceof the photosensitive drum 12 after the development and transfer of theimage.

The toner visualizing the image on the photosensitive drum 12 istransferred to the paper transported from the sheet feed unit 2. Thetransfer unit 15 used for this is a mechanism for transferring the tonerimage onto the paper by the application of an electric field of theopposite polarity to the toner. For example, when the electrostaticimage has negative charge, the polarity of the electric field applied tothe transfer unit 15 is positive.

The transfer unit 15 of the image forming apparatus comprises a transferbelt stretched between rollers, such as a driving roller and a drivenroller, and having a predetermined resistance value. A transfer rollercapable of applying a transfer electric field is disposed in the contactsection between the photosensitive drum 12 and the transfer belt. Thetransfer roller has electrical conductivity and elasticity, and thephotosensitive drum 12 and the transfer belt are brought into surfacecontact with each other by a predetermined width (transfer nip) by thefunction of the transfer roller. Hence, the transfer efficiency to thepaper being transported is improved. The paper to which the toner imagehas been transferred by the transfer unit 15 is transported to thefixing unit 16 disposed on the downstream side in the paper feeddirection.

The fixing unit 16 comprises a heat roller and a press roller, melts theunfixed toner on the transported sheet by heating the toner with thetemperature of the surface of the heat roller, and fixes the toner imageon the sheet with the pressing force of the press roller in thepress-contact section (fixing nip) between the heat roller and the pressroller.

The paper feed unit 2 includes paper feed cassettes 21 a to 21 d forstoring paper of different types and sizes, a large-capacity paper feedcassette 22 capable of storing a large amount of paper of regular size,and a manual paper feed unit 23 for mainly picking up paper of irregularsize.

The paper supplied from the paper feed unit 2 is transported to a resistroller 18 by the function of transport rollers provided along apredetermined path. The sheet that has reached the resist roller 18 isonce stopped, and the resist roller 18 is rotated again at the timing ofaligning the front end of the stopped paper and the toner image on thephotosensitive drum 12. At this time, the toner image on thephotosensitive drum 12 is transferred to the paper by the function ofthe transfer unit 15. The paper to which the toner image has beentransferred is guided to the fixing unit 16, and the toner image on thepaper is fixed as an image. The paper on which the image has been fixedis discharged onto a paper output tray 20 by the function of a paperdischarge roller 19.

The following will explain the structure and operation of the manualpaper feed unit 23 according to this embodiment. FIG. 4 is explanatoryviews for explaining the structure of the manual paper feed unit 23according to this embodiment. The manual paper feed unit 23 comprises amanual feed tray 230 capable of storing a plurality of sheets of paperof a size and material desired by the user; a paper regulating plate 231for regulating the paper position in a direction orthogonal to the paperfeed direction with respect to the manual feed tray 230; a pickup roller232 for picking up the topmost sheet of the paper stored in the manualfeed tray 230; a paper feed roller 234 for feeding the paper picked upby the pickup roller 232 from the manual feed tray 230 to a downstreamtransport path 221 for supplying the paper to a print section; and areverse roller 235 for separating sheets when a multi-feed occurs.

The pickup roller 232 is mounted to an end of an arm section (not shown)supported on the rotation shaft of the paper feed roller 234. The pickuproller 232 does not reach the feed point of the loaded paper and waitsabove the feed point until the normal feed timing. A drive coupling ismade by an electromagnet etc. supported on the rotation shaft of thepaper feed roller 234 which rotates upon a paper feed request, a drivebelt 233 which links the paper feed roller 234 and the pickup roller 232rotates, and the pickup roller 232 is lowered to the feed point by therotational moment. The topmost sheet of the loaded paper is taken out ofthe manual feed tray 230 by the friction with the surface of the pickuproller 232.

The paper taken out by the pickup roller 232 passes over a paper guide220 provided between the paper feed roller 234 and the manual feed tray230, and reaches the press-contact section between the paper feed roller234 and the reverse roller 235. The paper which has reached thepress-contact section is fed to the transport path 221 on the downstreamside by the function of the paper feed roller 234.

The reverse roller 235 is placed in a state in which it is pressedagainst the paper feed roller 234. The reverse roller 235 has a functionof rotating in a direction reverse to the paper feed direction when amulti-feed occurs and retracting an extra sheet fed by the multi-feed(that is, a sheet fed together with a sheet intended to be transported)to the manual feed tray 230. Whether or not the reverse roller 235 is tobe rotated in the reverse direction is determined as follows.

Specifically, a torque limiter 206 (see FIG. 8) is supported on adriving shaft 235 a of the reverse roller 235. When one sheet is fed,the drive load of the torque limiter 206 is small and a coupling to adrive source 204 b is not made (see FIG. 8). Thus, the reverse roller235 is rotated by the transport force of the transported paper andapparently feeds the transported paper to the transport path 221together with the paper feed roller 234. On the other hand, if amulti-feed occurs and plural sheets of paper are transported, whenplural sheets of transported paper enter into the press-contact sectionbetween the paper feed roller 234 and the reverse roller 235, the loadof the torque limiter 206 increases, a coupling to the drive source 204b is made, the reverse roller 235 is rotated in the direction reverse tothe rotation direction of the paper feed roller 234 as the driving shaft235 a of the reverse roller 235 turns, and the sheet on the reverseroller 235 side (the extra sheet fed by the multi-feed) is returned tothe manual feed tray 230. In short, the sheet retracting unit 250according to the present application comprises the reverse roller 235and the torque limiter 206, and is designed to drive the reverse roller235 and retract the transported sheet to the upstream side in the paperfeed direction when simultaneous feeding of multiple sheets oftransported paper is detected by a later-described multi-feed detectingsection 205 (see FIG. 8).

Disposed in the manual feed tray 230 is a paper regulating plate 231 forpreventing paper from being wrinkled or torn and missing of a part ofprinted image due to skew of the transported paper by adjusting thepaper position in a direction orthogonal to the paper feed direction ofthe loaded paper. The paper regulating plate 231 is connected to therack/pinion gear so that it is movable according to the paper size andslidable with respect to the manual feed tray 230. On the other hand,for the position of the rear end of the loaded paper, no member forregulating the position is provided. As shown in FIG. 8, the manual feedtray 230 is mounted in an inclined manner so that its end on theapparatus side is lower and the other end on the paper rear-end side ishigher, and thus the position of the front end of the loaded paper isnaturally determined.

In the manual feed unit 34 having such a structure, after occurrence ofmulti-feed, when the paper is returned to the manual feed tray 230 bythe function of the reverse roller 235, the above-mentioned problemoccurs. In other words, when a multi-feed occurs, the sheet on thereverse roller 235 side is returned to the upstream side in the paperfeed direction, but if the sheet is returned upstream of the paper feedpoint of the pickup roller 232 by the returning force of the reverseroller 235, the sheet under the returned sheet (the next sheet intendedto be transported after the returned paper) is taken out by the pickuproller 232 in the next paper feeding process and transported togetherwith the paper returned to the top of that paper, and therefore there isan extremely high possibility of multi-feed.

The condition of multi-feed occurred at this time is very bad, and whenthe lower sheet is held between the paper feed roller 234 and thereverse roller 235, the load of the torque limiter 206 does not increaseand the lower sheet enters into the transport path 221, but when theupper sheet advances to a position where the upper sheet is held betweenthe paper feed roller 234 and the reverse roller 235, the load of thetorque limiter 206 increases. As a result, the reverse roller 235 startsrotating in the reverse direction. However, since the function of thereverse roller 235 is to return the front end of the paper fed by themulti-feed with the returning force of the reverse roller 235, thereverse roller 235 does not have a sufficient transport force fortransporting the lower sheet. Therefore, even when the upper sheetpasses through the transport path by the rotation force of the paperfeed roller 234, the lower sheet stays in a state in which it is heldbetween the paper feed roller 234 and the reverse roller 235, and apaper entry sensor, not shown, is kept in an on-state. As a result, atransport jam is caused and the apparatus is stopped.

In order to solve such a problem, in this embodiment, a paper pressmember 240 is provided between the paper feed roller 234 and the manualfeed tray 230. FIGS. 5A and 5B are schematic views showing the structureof the paper press member 240. FIG. 5A shows a partial cross sectionseen from a direction orthogonal to the paper feed direction, and FIG.5B shows a partial cross section seen from the paper feed direction. Thepaper press member 240 comprises a contact member 241 capable of cominginto contact with paper passing through the upper surface of the paperguide 220, and a solenoid 242 for advancing and retracting the contactmember 241 from an aperture 220 a formed in the paper guide 220.

The contact member 241 is made of elastic material, such as rubber, foamsponge and cork, so that it has a predetermined width in a directionorthogonal to the paper feed direction and a semicircular cross section.When the paper is transported normally, the contact member 241 islocated under the paper guide 220 and does not come into contact withthe passing paper. On the other hand, when a multi-feed is detected andthe paper is to be retracted to the manual feed tray 230 by the functionof the reverse roller 235, the contact member 241 is moved up by theoperation of the solenoid 242 to cause a part of the contact member 241to project from the aperture 220 a of the paper guide 220, so that thecontact member 241 and the retracted paper come into contact with eachother. The projecting amount of the contact member 241 from the aperture220 a is controlled by the operation of the solenoid 242. When theprojecting amount is increased, the friction force between the contactmember 241 and the paper being retracted increases, and the retractingamount to the upstream side in the paper feed direction is reduced. Onthe other hand, when the projecting amount is decreased, the frictionforce between the contact member 241 and the paper being retracteddecreases, and the retracting amount to the upstream side in the paperfeed direction is increased. In this application, the projecting amountof the contract member 241 from the aperture 220 a is adjusted so that,when the paper is retracted, the paper end (the front end in the feeddirection) does not return upstream of the paper feed point of thepickup roller 232.

The following will explain the operation of the manual paper feed unit23 when a multi-feed occurs. FIGS. 6A to 6C and FIGS. 7A to 7C areexplanatory views for explaining the operation performed by the manualpaper feed unit 23 when a multi-feed occurs. Before a paper feed requestis made, as shown in FIG. 6A, the pickup roller 232 is in a standbystate above the paper feed point. When a paper feed request is made, thedrive belt 233 which links the paper feed roller 234 and the pickuproller 232 is rotated and the pickup roller 232 is lowered to the paperfeed point by the rotation moment.

A topmost sheet P1 among the paper loaded in the manual feed tray 230 istaken out of the manual feed tray 230 by the function of the pickuproller 23 which has reached the paper feed point, and, if anelectrostatic force acts between the topmost sheet P1 and a sheet P2below, the sheet P2 is also transported together with the sheet P1 (FIG.6B). Thus, when a plurality of sheets P1 and P2 enter into thepress-contact section between the paper feed roller 234 and the reverseroller 235, a multi-feed occurs (FIG. 6C).

When a plurality of sheets P1 and P2 enter into the press-contactsection between the paper feed roller 234 and the reverse roller 235,the driving load of the reverse roller 23 is increased compared to thatin transporting one sheet, and therefore the load of the torque limiter206 supported on the driving shaft 235 a of the reverse roller 235increases. Hence, the reverse roller 235 is coupled to the drive source204 b for driving the reverse roller 235, so that the drive force istransmitted to the reverse roller 235, and the reverse roller 235 isrotated in the opposite direction to the rotating direction of the paperfeed roller 234 (FIG. 7A).

When it is recognized that the reverse roller 235 is drive-coupling, thesolenoid 242 of the paper press member 240 located under the paper guide220 is activated to cause a part of the contact member 241 to projectupward from the upper surface of the paper guide 220 (FIG. 7B). Thecontact member 241 projecting upward from the upper surface of the paperguide 220 comes into contact with the back surface of the sheet P2returning to the manual feed tray 230 by the function of the reverseroller 235, the friction force between them acts as a load with respectto the returning force, and the return amount is reduced compared tothat when there is no load. As a result, the position of the front endof the retracted sheet P2 is prevented from returning upstream of thepaper feed point of the pickup roller 232, and the sheet P2 is taken outof the manual feed tray 230 in the next paper feeding process (FIG. 7C),thereby preventing reoccurrence of multi-feed.

FIG. 8 is a block diagram showing the structure of a control system ofthe manual paper feed unit 23. The manual paper feed unit 23 comprises acontrol section 200 composed of a microcomputer etc., and controls thepaper feeding process. Connected to the control section 200 is an I/O201 for inputting and outputting signals for sending and receivingvarious kinds of information to/from the printer unit 1; an I/O 203 forinputting and outputting signals for sending and receiving various kindsof information to/from the scanner unit 3; the drive section 204 a fordriving the drive source 204 b of the paper feed roller 234 etc.; amulti-feed detecting section 205 for detecting a multi-feed occurring inthe press-contact section between the paper feed roller 234 and thereverse roller 235; and the paper press member 240 for reducing thetravel amount of the paper to be retracted in the event of a multi-feed.

FIG. 9 is a flowchart showing the steps of the paper feeding processperformed by the manual paper feed unit 23. First, the control section200 determines whether or not there is a paper feed request bydetermining whether or not a paper feed start signal has been inputtedfrom the printer unit 1 through the I/O 201 (step S11). When there is nopaper feed request (S11: NO), the control section 200 waits until apaper feed request is made.

When determined that there is a paper feed request (S11: YES), thecontrol section 200 drives the paper feed roller 234 and pickup roller232 by instructing the drive section 204 a to drive the drive source 204b (step S12), and transports the paper taken out of the manual feed tray230 (step S13).

Next, the multi-feed detecting section 205 determines whether or not thetorque limiter 206 was activated and the reverse roller 235 was rotatedin the reverse direction (step S14). When the torque limiter 206 is notactivated and the reverse roller 235 is not rotated in the reversedirection (S14: NO), the control section 200 can determine that amulti-feed does not occur and therefore continues the paper feedingprocess (step S18).

When determined that the torque limiter 206 was activated and thereverse roller 235 was rotated in the reverse direction (S14: YES), themulti-feed detecting section 205 determines that a multi-feed wasdetected (step S15) and reports the detection result to the controlsection 200.

When the control section 200 receives the report indicating that themulti-feed detecting section 205 detected a multi-feed, it raises thepaper press member 240 by activating the solenoid 242 of the paper pressmember 240 (step S16). Then, the control section 200 transports theupper sheet located on the paper feed roller 234 side to the downstreamside in the paper feed direction and transports the lower sheet locatedon the reverse roller 235 side to the upstream side in the paper feeddirection (step S17), and continues the paper feeding process (S18).

Next, the control section 200 determines whether or not there is a sheetto be supplied next (step S19). When determined that there is a sheet tobe supplied next (S19: YES), the control section 200 returns the processto step S12. When determined that there is no sheet to be supplied next(S19: NO), the control section 200 moves into a standby state and waitsfor the input of a new paper feed start signal (step S20).

Note that although this embodiment explains the manual feed tray 23 ofthe printer unit 1, the present application is of course applicable to apaper feed unit of the automatic document feeder 35 mounted in thescanner unit 3.

As this application may be embodied in several forms without departingfrom the spirit of essential characteristics thereof, the presentembodiment is therefore illustrative and not restrictive, since thescope of the application is defined by the appended claims rather thanby the description preceding them, and all changes that fall withinmetes and bounds of the claims, or equivalence of such metes and boundsthereof are therefore intended to be embraced by the claims.

1. A sheet feeder comprising: a sheet storing section for storingsheets; a paper feed roller for feeding a sheet taken out of said sheetstoring section to a predetermined supply destination; a detectingsection for detecting a multi-feed in said paper feed roller; a sheetretracting unit for retracting, when said detecting section detects amulti-feed of sheets, an extra sheet fed by the multi-feed to anupstream side in a sheet feed direction; and a contact memberconfigured, between said paper feed roller and a front end in the sheetfeed direction of the sheet stored in said sheet storing section, sothat said contract member is capable of advancing and retracting andcapable of coming into contact with an extra sheet fed by a multi-feed.2. The sheet feeder according to claim 1, wherein said contact membercomes into contact with a front surface or a back surface of the extrasheet when retracting the sheet.
 3. The sheet feeder according to claim1, further comprising a driving section for moving, when feeding a sheetto the supply destination, said contact member not to come into contactwith the sheet, and for moving, when said detecting means detects amulti-feed of sheets, said contact member to come into contact with theextra sheet fed by the multi-feed.
 4. The sheet feeder according toclaim 1, wherein said sheet retracting unit includes a reverse rollerplaced opposite to said paper feed roller, and a torque limitersupported on a driving shaft of said reverse roller, wherein when saidtorque limiter detects an increase in load and said reverse roller iscoupled to a drive source and starts to be driven, said detectingsection determines that a multi-feed of sheets is detected.
 5. The sheetfeeder according to claim 1, wherein a travel amount of sheet whenretracting the sheet by said sheet retracting unit is restrained by thecontact between the sheet and the contact member.
 6. The sheet feederaccording to claim 5, further comprising a pickup roller arranged to beable to come into contact with the sheet stored in said sheet storingsection, wherein the sheet feeder restrains a front end in the feeddirection of the sheet to be retracted from returning upstream of acontact section between said pickup roller and the sheet stored in saidsheet storing section.
 7. The sheet feeder according to claim 1, whereinsaid contact member has elasticity.
 8. The sheet feeder according toclaim 1, wherein said sheet storing section is a manual feed tray.
 9. Animage reading apparatus comprising: a sheet feeder as set forth in claim1; and an image reading section for reading an image recorded on a sheetfed by said sheet feeder.
 10. An image forming apparatus comprising: asheet feeder as set forth in claim 1; and an image forming section forforming an image on a sheet fed by said sheet feeder.